Cross reference is made to Disclosure Document No. 431,861, titled xe2x80x9cEnergy Saving Air Conditioning or Refrigeration Systemxe2x80x9d of Robert Levenduski and James Marsh Lester, dated Feb. 16, 1998 and received in the U.S. Patent and Trademark Office on Feb. 26, 1998.
The present invention relates to a method and apparatus for air conditioning systems which involves a thermal storage unit and in particular to a unit which can store heat when ambient air temperature is high and release stored heat directly to ambient air when the ambient air temperature is lower.
A typical refrigeration circuit such as the type used for air conditioning, refrigeration and the like, includes, among other components, a condenser unit for removing heat from the working fluid, such as Freon. In a typical house or building air conditioning system, the condenser is placed outdoors and includes an arrangement of tubing, often coupled to fins, or other heat dispersing units, and often provided with a fan or similar device for providing air flow over the coils and fins. In this way, heat may be transferred from the working fluid substantially directly (i.e., by heat traveling only through the walls or surfaces of the coils or fins) to the ambient air. Because heat flows only from warmer to cooler bodies, the working fluid can be cooled, in such condenser, only if the temperature of the working fluid is higher than the temperature of the ambient air. When the ambient air temperature is relatively high, such as on summer afternoons when air conditioning is likely to be used, it may be necessary to provide relatively high compression of the working fluid in order to achieve a working fluid temperature which exceeds ambient air temperature. Such high compression can be relatively energy consumptive creating high demand for electrical energy. In many situations, energy is priced such that its cost is higher during high demand times and accordingly traditional air conditioning systems can be relatively expensive to operate.
One approach to this situation has been to provide a system in which working fluid heat is stored in a thermal storage medium such that the storage medium can be cooled, using a refrigeration process, at a later time. Although this approach may provide certain benefits, it requires the use of a refrigeration unit, and thus the consumption of electrical power, for cooling the heat storage medium, albeit, possibly at a time of lower ambient air temperature. The consumption of electricity for a refrigeration process (e.g. to run a compressor) can be undesirably costly. Accordingly, it would be useful to provide a system which can store some or all condenser heat, e.g., during high ambient air temperature periods, without the need for using a refrigeration unit for cooling the heat storage medium. It would further be advantageous to provide a system which provides an efficient heat transfer system with radiant fins and other heat exchanging means to cool the storage medium during non-peak operating hours, i.e. at nighttime.
The present invention includes a recognition of certain problems in previous approaches including as described herein. According to one aspect of the invention, heat from the condenser coils of an air conditioning unit can be stored in a heat storage medium, preferably by melting or otherwise changing phase of some or all of the medium. Preferably, such heat storage occurs when ambient air temperature is relatively high, such as exceeding a first threshold temperature. At a later time, such as when ambient air temperature is below a second threshold temperature, the heat storage medium is cooled, not by a refrigeration cycle, but by transferring heat directly to the ambient air, e.g., blowing ambient air around containers of the heat storage medium. In this way, the heat storage medium can be cooled, for reuse in the next high-air-temperature cycle, but without the need for using refrigeration for cooling the working fluid.
Although the present invention can be implemented with a variety of heat storage materials, it is preferred to use a material which can take advantage of latent heats of phase change such as latent heats of melting and freezing. In one embodiment, a material is provided which is relatively inexpensive, has a melting/freezing point occurring at temperatures similar to temperatures found during night time ambient air temperatures and which also has a relatively high latent heat of melting/freezing. In one embodiment, the heat transfer material is a calcium chloride hydrate.
Preferably the system is configured so that it is relatively inexpensive to design, fabricate, operate, maintain or repair. In one embodiment, the heat storage material is encapsulated in containers which are sized shaped and positioned, relative to other components, to achieve both the melting and the freezing of the heat storage material in-place (i.e., without the need to pump or transfer heat storage material from a melting location to a freezing location) and preferably such that the system can be relatively easily, and preferably automatically, changed from the melting configuration to the freezing configuration. In one embodiment, a valve or switch responds to temperatures in excess of a first ambient air threshold temperature to shunt working fluid from an ordinary air-cooled condenser coil to a coil in contact with the heat storage medium. In one embodiment, the system responds to a temperature which is below a second threshold temperature, by using a simple switch or valve to provide desired air flow for cooling the heat storage medium such as by activating a fan or blower.
In this way, a system according to the present invention can not only relieve some or all of the compressor burden normally imposed by high ambient air temperatures (thus reducing operating energy consumption and, possibly reducing wear on compressor components) but also reduce energy costs by reducing the amount of energy which is consumed during relatively high-energy-cost periods.
In one aspect of the present invention, a thermal energy storage unit is provided in connection with an air conditioning or refrigeration condenser. Working fluid waste heat is stored in the thermal energy storage unit during at least a relatively hot part of the day. Heat stored in the thermal energy storage unit is then rejected to the air during a cooler period, such as night. By rejecting the stored heat directly to the atmosphere, there is no need to provide an energy-consumptive refrigeration cycle for cooling the thermal storage medium material. In this way, a refrigeration system compressor has a reduced load and/or reduced duty cycle during hot parts of the day and relatively less energy can be used during high-demand times when energy may be more expensive.
In another aspect of the present invention, a self-contained heat storage and heat exchanger system is provided which is placed adjacent to or stacked below or above an existing air conditioning unit. In this embodiment, the desired heat transfer from the hot working fluid in the air conditioning system would be attained through another heat transfer step between the working fluid and a separate coolant loop in the self-contained system. The use of a self-contained system would require fewer modifications to an existing air conditioning system and would further facilitate retrofitting previously installed air conditioning systems. Alternatively, new installations would be installed incorporating both the typical air conditioning unit and the self contained thermal storage unit in one packaged system ready for installation.
In one embodiment of the present invention, the hot working fluid is placed in thermal communication with the coolant of the self-contained unit, and the heat from the working fluid is then transferred to the thermal storage medium. During off-peak nighttime hours, when ambient air temperature is cooler, the heat energy stored in the thermal storage medium is transferred to the cooler ambient air. As a result of the cooler working fluid in the air conditioning unit, higher efficiencies are obtained.
It is yet another aspect of the present invention to improve the transfer of heat between the fluid in the thermal storage unit and the thermal storage medium. By employing a plurality of tubes and fins or parallel heat exchanging plates immersed in the thermal storage medium, more of the thermal storage medium""s surface area will be exposed to the hot liquid in the coolant loop.
Thus in one aspect of the present invention a method for providing reduced energy consumption of a cooling unit for cooling at least a first space, the cooling unit having at least a compressor, for compressing a working fluid, a condenser and an evaporator, the method comprising:
transferring at least first heat from said working fluid to a second fluid;
placing said second fluid in thermal communication with a first change-of-phase heat storage material having a first temperature whereby at least some of said first change-of-phase material changes from a first phase to a second phase and absorbs latent heat, and wherein said first phase is substantially solid and said second phase is substantially liquid;
transferring heat from said change-of-phase material to the ambient air whereby at least some of said change-of-phase material changes phase from said second phase to said first phase and releases latent heat.